Your computer is probably getting slower and slower if you don't have Anti-Spyware software.  Spyware can steal sensitive data and keep programs from working properly.  Make sure you have at least 1 program installed and that the definitions are up to date.  Try:

                                        SpyBot Search and Destroy

 

Virus Protection Software is also important.  Keep your subscription current and the definitions.  It's much cheaper than getting your computer fixed!